(a) Field of the Invention
The present invention relates to a stabilizing composition being useful for improving the stability of reagent for redox reaction, and a reagent composition for redox reaction having an improved stability. The reagent composition for redox reaction can be applied for a reagent for electrochemical biosensor.
(b) Description of the Related Art
The periodic measurement of a blood glucose level is important to managing the diabetes, and has been performed by using various electrochemical biosensors with precision and accuracy. The electrochemical biosensor for measuring the blood glucose level is manufactured by applying a reagent including enzyme, electron transfer and various stabilizers and dispersant to the working electrode and drying the working electrode applied with the reagent. The most important factors affecting the characteristics of electrochemical biosensor are the properties of the enzyme and the electron transfer.
For example, FAD-GOx (flavin adenine dinucleotide-glucose oxidase) used for most commercially-available electrochemical sensor as a glucose oxidoreductase has a heat stability and a reaction specificity to oxidize only glucose, but tends to show a large fluctuation in the measured values on the blood sources such as venous blood, arterial blood and peripheral blood, by using the sensor adopting the FAD-GOx, because the enzyme reacts with oxygen dissolved in blood.
Meanwhile, the sensor adopting pyrrole quinolone quinone-glucose dehydrogenase (PQQ-GDH) is not nearly affected by the blood oxygen, but shows the specificity to monosaccharides such as mannose, maltose and lactose, or disaccharides. In particular, it has been reported that the sensor can cause the faculty medical practice due to the influence of maltose in a patient with kidney peritoneal dialysis. The sensor adopting nicotinamide adenine dinucleotide-glucose dehydrogenase (NAD-GDH) shows better reaction specificity than PQQ-GDH, because it does not react with the disaccharides such as mannose, maltose and lactose, but has a disadvantages of need of NAD or NADP as cofactor and a low storage stability.
Recently, the electrochemical sensor using flavin adenine dinucleotide-glucose dehydrogenase (FAD-GDH) has been wildly used, because it is not affected by the amount of blood oxygen, has a high stability and does not have a specificity to maltose unlike PQQ-GDH. However, FAD-GDH can use limited kinds of electron transfers (mediator) according to the kinds of bacteria or fungi producing the enzyme.
Potassium ferricyanide [K3Fe(CN)6] is used universally as the electron transfer. It is cheap and is useful for the sensors adopting FAD-GOx, PQQ-GDH or FAD-GDH due to a high reactivity. However, the sensor using Potassium ferricyanide as the electron transfer can show the measurement error caused by an interfering substance such as uric acid or gentisic acid in blood, and must be manufactured and stored with a special caution due to the deterioration caused by the temperature and humidity. In addition, because the ground current changes after being stored in a long time, it has a difficulty in accurate detecting a low concentration of glucose.
Hexaammineruthenium chloride [Ru(NH3)6Cl3] has a better redox stability, compared to ferricyanide. The sensor employing hexaammineruthenium chloride as an electron transfer can be prepared and stored easily and a small change in the ground current after being stored in a long time. However, hexaammineruthenium chloride cannot be used together with FAD-GDH, resulting in the difficulty in manufacturing a commercially-useful sensor.
Recently, there are several attempts to detect the blood glucose by using special types of biosensors which employ the electrode with nanopore surface without including enzyme and electron transfer. For examples, U.S. Pat. No. 8,083,926 presents the method of detecting a low concentration of glucose by using the electrode with cyclodextrin nanopore. The sensor cannot be suitable for detecting a very small amount of glucose, and for mass production of sensor.
Therefore, a reagent for redox reaction, or more specifically a reagent for redox reaction useful for electrochemical biosensor has no affection of oxygen, a small range of performance variation being caused by the temperature, the humidity and the long-term storage, detection of a wide range of glucose concentration, and suitability for mass-production, is still required. The present invention provides a biosensor reagent composition satisfying the requirements.